1. Field of the Invention
This invention relates generally to systems for determining the spatial orientation (i.e., the azimuth and elevation) of a movable apparatus.
2. Description of the Related Art
There are many circumstances in which it is useful or necessary to determine the spatial orientation—i.e., the azimuth and elevation—of a movable apparatus. For example, in order to establish or determine particular property lines or boundaries, it is essential to know the spatial orientation of the equipment used in a surveying application. Similarly, for weaponry such as a mortar which must be aimed, it is vital to know the spatial orientation of the weapon prior to its being fired.
Numerous devices and systems have been employed to establish spatial orientation. For example, a digital magnetic compass can be used; however, such a compass can be susceptible to magnetic interference, and its azimuth accuracy is typically limited to about 9 mils (RMS). A high performance gyrocompass could be employed, though this device may be unacceptably bulky and expensive. A compact gyrocompass or inertial measurement unit (IMU) might also be used, though these devices tend to drift, which can limit their operation time. A differential global positioning system (DGPS) is another possible approach. However, this method may be limited by the availability of the GPS signal and the need for a long baseline. Furthermore, use of these methods is difficult when the measurement device must be attached to a weapon such as a mortar because of the high shock environment during weapon firing, and the need for a compact lightweight device.